The present invention relates to micromotors using electro-sensitive movable fluids (electro-conjugate fluid, ECF) which move between electrodes upon application of a voltage, and more particularly to extremely thin micromotors using the electro-sensitive movable fluids. The invention also relates to linear motors using the electro-sensitive movable fluids. The invention further relates to micropumps using the electro-sensitive movable fluids, methods of using the micropumps and microactuators using the micropumps as cooling means. The present invention furthermore relates to methods of controlling flow properties of substantially dielectric fluids by applying a voltage and apparatuses for controlling flow properties of fluids.
It is known that the characteristics of certain kinds of dielectric fluids vary when the dielectric fluids are subjected to electric fields. In case of liquid crystals, for example, when a voltage is applied to liquid crystal compounds, orientation properties of the compounds are varied to thereby vary light transmittance of the compounds. It is also known that, when a voltage is applied to heterogeneous fluids containing particles or the like, properties of the fluids such as viscosity are varied by Winslow Effect.
There are, however, problems in the fluids whose properties are varied upon application of a voltage. For example, the liquid crystal compounds are very expensive, or the heterogeneous fluids show poor dispersion stability.
The present inventors have found such a novel effect that some specific fluids move upon application of a voltage, and already applied for patents on the specific fluids (electro-sensitive movable fluids) and micromotors using the electro-sensitive movable fluids (see: Japanese Patent applications No. 16871/1996, No. 16872/1996, No. 76259/1996, No. 248417/1996 and No. 241679/1996), which form the basis of U.S. patent application Ser. No. 08/792,544, filed Jan. 31, 1997. The micromotors described in these publications show increased output power when they are miniaturized.
In order to more efficiently drive the micromotors disclosed in the above publications, they should be improved for the miniaturization. The motors described in the publications are those of rotor rotation type, and any linear motor which is linearly driven is not described. Further, any pump using the electro-sensitive movable fluid is not described either.
When a voltage is applied to an electro-rheological fluid (ER fluid), its hydrodynamic properties such as viscosity greatly vary reversibly at a high speed correspondingly to the applied voltage. The fluids showing these properties are broadly divided into heterogeneous type (particle dispersion type) and homogeneous type. As the heterogeneous ER fluid, a dispersion obtained by dispersing fine particles such as silica gel in an insulating oil is known.
The heterogeneous ER fluids, however, have a problem in that sedimentation or flotation of particles takes place because of a difference in specific gravity between the particles and the medium. Even if the particles and the medium have the same specific gravity, the same problem of sedimentation or flotation of particles takes place with time because the temperature dependence of the specific gravity of the particles and that of the specific gravity of the medium are different from each other at low or high temperatures. Moreover, the dispersed particles of the heterogeneous ER fluid form a chain structure when a voltage is applied, and therefore, the hydrodynamic properties of the fluid are changed. With the formation of the chain structure, not only increase of viscosity but also development of elasticity takes place, and the fluid exhibits mechanical response approximate to a solid state. For this reason, linear control of the heterogeneous ER fluids is difficult, and in many cases, complicated control means such as feedback control is necessary.
Of the homogeneous ER fluids, a liquid crystal is known as an ER fluid which exhibits no elasticity. The homogeneous ER fluids have ease of controlling because they exhibit no elasticity even when a voltage is applied, and they are free from problems of particle sedimentation and particle flotation because they are homogeneous. However, the homogeneous ER fluids such as liquid crystals are very expensive, so that they are not broadly employed for an industrial use, liquid crystals are only used for, for example, display devices of extremely high value added. Further, the liquid crystals which are the homogeneous ER fluids can be driven only in such a temperature range that the liquid crystals are in the liquid crystal state, so that the temperature range wherein the liquid crystals can be used as the ER fluids is extremely narrow. Though the estimated temperature range wherein the ER fluids are used is from about xe2x88x9230xc2x0 C. to about 120xc2x0 C., the liquid crystals cannot be driven in such a wide temperature range.
As described above, the homogeneous ER fluids are advantageous as the ER fluids from the control viewpoint, but they are very expensive and their working temperature range is narrow. On the other hand, the heterogeneous ER fluids are relatively inexpensive, but they are difficult to control and have a problem of fluid stability such as occurrence of particle sedimentation or particle flotation.
In the paper No. 62-252, pp. 437-438, of the 8th symposium on xe2x80x9cDynamics Relating to Electromagnetic Forcexe2x80x9d, there is description about xe2x80x9cResearches on Electrostatic Devices (New Stress-Transfer System Using Fibers)xe2x80x9d. The particles dispersed in the heterogeneous ER fluid form a chain structure when a voltage is applied to the heterogeneous ER fluid, as described above. This mechanism is applied to the electrostatic devices of the above paper. That is, instead of the particles, an electrode provided with woven fabric on its surface is used in a silicon oil, and a voltage is applied to the xe2x80x9cwoven fabric electrodexe2x80x9d, whereby a chain structure equivalent to the particle chain structure of the heterogeneous ER fluid containing particles is formed by the woven fabric to thereby develop hydrodynamic properties of the ER fluid. In other words, instead of using an ER fluid containing particles, using a silicon oil woven fabric free from sedimentation or flotation is bonded to an electrode material and the woven fabric is used as an electrode. By the application of a voltage, fibers of the woven fabric are allowed to stand up, and dynamic resistance of the upstanding woven fibers is produced to control the fluid. Further, the manuscript collection (pp. 203-206) of the 39th Automobile Control Association lecture meeting (Oct. 16, 17, 18, 1996) discloses xe2x80x9cNew Torque-Transfer System Using Fibersxe2x80x9d, and describes that, when fabric is adhesion bonded to a circular plate and the circular plate is rotated in an electric field, the shear stress is increased.
In the above methods, it is explained that the woven fabric has a rigid structure upon application of a voltage and is orientated in the direction of the electric field thereby to increase the shear stress. In the methods, therefore, the woven fibers which are swayed by the fluid when no voltage is applied are made rigid and orientated by applying a voltage, so that the fibers can resist the relative motion of the fluid to the electrodes, whereby increase of sheer stress during application of a voltage is accomplished. In the methods, accordingly, only a silicon oil is used, and hydraulic oil constituting a machine part or a working mechanism is never employed, further applicability of the methods to a mechanism.
In the above methods, further, the conductive electrode material is not exposed at all and is evenly covered with the woven fabric. Moreover, there is no report about production of a jet flow. It is described that the fibers of the woven fabric are swayed in the non-electric field according to the shear rate. Accordingly, flow property control mechanism of the above methods is different from the mechanism of the invention invented by the present inventors, that is, the shear stress is produced by virtue of formation of a jet flow. The shear stress produced in the present invention has hydrodynamic continuity, is free from yield stress which indicates solidification and has ease of controlling, while the above-mentioned fixed electrodes provided with woven fabric do not show these properties.
It is an object of the present invention to provide an extremely small-sized rotary motor and linear motor each of which is driven by a jet flow of an electro-sensitive movable fluid produced upon application of a direct-current-voltage and to provide a micropump using the electro-sensitive movable fluid.
It is another object of the invention to provide a novel method of using the above-mentioned micropump.
It is a further object of the invention to provide a microactuator using the above-mentioned micropump as a cooling means.
It is a still further object of the invention to provide a method of easily controlling flow properties of a dielectric fluid in a wide temperature range, said fluid being a homogeneous fluid free from sedimentation or flotation of particles, and to provide an apparatus employable in the method.
The micromotor (thin micromotor) according to the invention is a micromotor comprising a container to be filled with an electro-sensitive movable fluid, a lid to close the container by being engaged with the open top of the container, a rotating shaft borne by a shaft hole provided at the center of the lid and a bearing section provided at the center of the bottom of the container, a rotator fixed to the rotating shaft and rotatable together with the rotating shaft, and electrodes which produce a jet flow of the electro-sensitive movable fluid upon application of a voltage, wherein the diameter of the rotator is larger than the maximum thickness of the rotator.
The thin micromotor of the invention is broadly divided into a SE type ECF motor (stator-electrode type electro-conjugate fluid motor) and a RE type ECF motor (rotor-electrode type electro-conjugate fluid motor) with respect to the position of the electrode provided therein. In the SE type ECF motor, the electrodes are provided on the upper surface of the bottom and/or the lower surface of the lid of the container (fluid container) and are in contact with the electro-sensitive movable fluid. In the RE type ECF motor, the electrodes are provided on the upper surface and/or the lower surface of the rotator.
The housing of the micromotor of the invention generally has a maximum diameter of 50 mm and a maximum height of several mm, and the micromotor is extremely small and particularly thin. In spite of such small size, the micromotor of the invention rotates at a high rotational speed of about several hundreds to several tens of thousands rpm.
The other micromotor according to the invention is a micromotor comprising a housing constituted of a container to be filled with an electro-sensitive movable fluid and a lid, an electro-sensitive movable fluid filled in the container, a rotor which rotates by detecting a motion of the electro-sensitive movable fluid that is moved upon application of a voltage, a rotating shaft to rotatably fit the rotor to the housing, and plural electrodes which produce a jet flow of the electro-sensitive movable fluid upon application of a voltage, wherein the rotor is rotatably fitted to the housing through the rotating shaft and at least one bearing means. This micromotor includes the following first to third micromotors.
The first micromotor (SE type ECF motor) of the invention is a micromotor wherein the rotor is a vane rotor having vanes for detecting a motion of the electro-sensitive movable fluid when the electro-sensitive movable fluid is moved.
The second micromotor (RE type ECF motor) of the invention is a micromotor wherein the rotor is a cylindrical rotor whose surface is provided with plural electrodes.
The third micromotor (cup type ECF motor) of the invention is a micromotor wherein the rotor is an open-bottom rotor having a cylindrical body whose bottom is made open so as to allow the electro-sensitive movable fluid to enter, and the plural electrodes are arranged on at least one surface selected from the group consisting of an outer surface of the open-bottom rotor, an inner surface thereof, an inner wall surface of the housing and a wall surface of the protruded bottom of the housing.
In the third micromotor (cup type ECF motor), the electrodes are arranged on at least one surface selected from the group consisting of an outer surface of the open-bottom rotor, an inner surface thereof, an inner wall surface of the housing and a wall surface of the protruded bottom of the housing. Therefore, the electrodes may be provided vertically on the inner wall surface of the housing as in the above-mentioned SE type ECF motor, or may be provided vertically on the side wall of the protruded bottom.
That is, the micromotor of the invention includes the SE type ECF motor, the RE type ECF motor and the cup type ECF motor that is a complex type of the SE type ECF motor and the RE type ECF motor. In the cup type ECF motor, the rotor is in the cylindrical form whose top is closed and whose bottom is open (in the form of a cup placed bottom upward), and hence this rotor is sometimes referred to as xe2x80x9copen-bottom rotorxe2x80x9d or xe2x80x9ccup rotorxe2x80x9d hereinafter.
By making the size of the micromotor of the invention smaller, the electric energy can be converted to rotational energy with much higher efficiency. For example, when a SE type ECF motor whose housing has an inner diameter of 4 mm is used, the efficiency indicated by the ratio of output energy/input energy has been confirmed to be at most 40%.
The linear motor according to the invention comprises an electro-sensitive movable fluid, a container which is a closed container containing the electro-sensitive movable fluid, a driving shaft extended from the container, a moving member which is linearly moved together with the driving shaft by virtue of a jet flow of the electro-sensitive movable fluid, and at least one pair of electrodes which produce the jet flow of the electro-sensitive movable fluid upon application of a voltage.
The linear motor of the invention is broadly divided into a SE type ECF linear motor (stator-electrode type electro-conjugate fluid linear motor), a PE type ECF linear motor (piston-electrode type electro-conjugate fluid linear motor)and a CE type ECF linear motor (complex-electrode type electrode-conjugate fluid linear motor), with respect to the position of the electrode provided therein.
In the SE type ECF linear motor, the container (fluid container) has an outer cylinder and an inner cylinder; the electrodes are arranged between the outer cylinder and the inner cylinder and function to form an ununiform electric field in the electro-sensitive movable fluid; and the jet flow of the electro-sensitive movable fluid produced between the outer cylinder and the inner cylinder upon application of a voltage between the electrodes is introduced into the inner cylinder to thereby move the moving member in the inner cylinder.
In the PE type ECF linear motor, the moving member comprises at least one pair of porous members through which the electro-sensitive movable fluid is able to pass; the pair of porous members are electrically insulated from each other and are fixed to the driving shaft; and an ununiform electric field is formed in the electro-sensitive movable fluid by applying a voltage to the porous members to thereby produce a jet flow of the electro-sensitive movable fluid, whereby the porous members are moved together with the driving shaft in the container by virtue of the reaction of the jet flow of the electro-sensitive movable fluid.
The CE type ECF linear motor is a complex type of the SE type ECF linear motor and the PE type ECF linear motor. In the CE type ECF linear motor, for example, the fluid container has an outer cylinder and an inner cylinder; at least one pair of electrodes are arranged in the inner cylinder, and function to form an ununiform electric field in the electro-sensitive movable fluid and further are reversible in their polarities; the moving member which is moved with the jet flow of the electro-sensitive movable fluid produced upon application of a voltage between the electrodes is arranged between the outer cylinder and the inner cylinder; and the moving member is united to the driving shaft extended from the container.
The micropump according to the invention comprises an electro-sensitive movable fluid and at least two electrodes which are arranged in such a manner that the electro-sensitive movable fluid is moved in the direction of one electrode to the other electrode upon application of a voltage.
The method of using a micropump according to the invention comprises the steps of arranging at least two electrodes in such a manner that an electro-sensitive movable fluid is moved in the direction of one electrode to the other electrode upon application of a voltage, applying a voltage to the micropump containing the electro-sensitive movable fluid, and producing a jet flow of the electro-sensitive movable fluid in the direction of a target.
The microactuator of the invention using the above-mentioned micropump as a cooling means comprises an expansion pump chamber, suction and discharge valves to suction and discharge a liquid from and to the outside by expansion and contraction of the expansion pump chamber, an expansion driving member made of a shape-memory alloy which is contracted by electric power supply to expand or contract the expansion pump chamber, and a micropump comprising an electro-sensitive movable fluid and at least two electrodes which are arranged in such a manner that the electro-sensitive movable fluid is moved in the direction of one electrode to the other electrode upon application of a voltage, said microactuator serving to cool the shape-memory alloy with the jet flow of the electro-sensitive movable fluid produced by the micropump.
The micropump of the invention is designed so that the electro-sensitive movable fluid is moved between the electrodes correspondingly to the voltage applied between the electrodes, and serves as a pump by virtue of the self-propelled electro-sensitive movable fluid under application of a voltage. If a jet flow of the electro-sensitive movable fluid in the direction of a target is produced and brought into contact with the target, the micropump of the invention can be used as a means to cool the target when the temperature of the target is higher than the temperature of the electro-sensitive movable fluid.
The method of controlling flow properties of a fluid according to the invention comprises the steps of arranging at least one pair of electrodes capable of forming an ununiform electric field in a fluid, applying a voltage between the electrodes to produce a jet flow of the fluid between the electrodes, and controlling flow properties of the fluid by the jet flow.
The apparatus for controlling flow properties of a fluid according to the invention includes in a fluid at least one pair of electrodes capable of forming an ununiform electric field, said electrodes being arranged in such a manner that a voltage can be applied between the electrodes and that a gap to be filled with the fluid is formed between the electrodes.
At least one of the electrodes is preferably an uneven surface electrode having a non-smooth surface, particularly preferably a flocked electrode.
If a pair of electrodes capable of forming an ununiform electric field in a fluid is arranged in the fluid and if a voltage is applied between the electrodes, a new flow (jet flow) of the fluid, such as a circulating flow, is produced. When the shear direction of the original motion of the fluid is at right angles to the newly produced jet flow of the fluid, it is presumed that resistance to the relative motion of the fluid in the shear direction is produced, that is, shear stress is increased.
When a certain kind of a dielectric fluid (i.e., xe2x80x9celectro-sensitive movable fluidxe2x80x9d referred to herein) is subjected to an electric field, an electric force is generated in the fluid owing to the ununiformity of electric conductivity and dielectric constant. In the direct-current electric field, the Coulomb force acting on space charge dominates the dielectrophoretic force. This Coulomb force causes hydrodynamic instability, resulting in occurrence of convection of the electro-sensitive movable fluid or a second motion of the fluid. These phenomena are known as xe2x80x9celectrohydrodynamic (EHD) effectsxe2x80x9d.
The micromotor, the linear motor and the micropump according to the invention use, as driving force, a motion (jet flow) of the electro-sensitive movable fluid produced upon application of a voltage to the fluid. These control the flow properties of a fluid by forming a new jet flow from at least one pair of electrodes capable of forming ununiform electric field in the fluid in a different direction, e.g. vertical and opposite direction, from that of the flowing fluid.
The present inventors consider that the motion of the electro-sensitive movable fluid is probably by virtue of the EHD effects, but they do not conclude that the phenomenon occurring in the invention is owing to the. xe2x80x9cEHD effectsxe2x80x9d.
The micromotor, the linear motor and the micropump of the invention are apparatuses advantageously used to take out the flow energy of the electro-sensitive movable fluid produced upon application of a voltage as a driving force. That is, they are apparatuses to form a jet flow of the dielectric fluid by application of a voltage and to take out the jet flow as driving force. The micromotor of the invention is extremely small, and it can be made thin. Besides, the micromotor can be driven at a high speed.